There is a need today for improving the emissions characteristics and efficiency of the internal combustion (IC) engine. The conventional four-stroke gasoline engine suffers from high air-intake throttling pumping losses at part-load, the typical automotive driving condition, while the two-stroke engine suffers from the opposite problem of requiring an air pump or blower to pressurize air for forcing into the cylinder during the very short duration of air-intake when pressures are above atmospheric. Both engines have a low expansion ratio, the four-stroke gasoline engine limited to approximately 9:1 because of the engine knock limitations of its compression stroke (which equals the expansion stroke), and the two-stroke limited to approximately 7:1 because of the need to open the exhaust valve early to expel the exhaust gases in time to take in the intake air charge in a very short time.
The diesel engine attempts to solve the pumping loss problem of the four-stroke gasoline engine by taking in a full intake charge (maximum amount of air) and controlling engine power by injecting varying amounts of fuel directly into the cylinder (to consume varying amounts of the intake air versus the entire amount of limited (throttled) air in the case of the gasoline engine). While the diesel has low part-throttle air-pumping losses it has high frictional losses due to its high compression ratio (of typically 16:1 to 24:1) and high in-cylinder heat transfer losses due to the high cylinder surface-to-volume ratio. Its constant pressure versus constant volume combustion reduces its Otto cycle efficiency. Also, having to take in a full charge of air at part load and moving it at high friction for the entire compression stroke of the high compression ratio is wasteful from the perspective of the present invention.
Most attempts to alleviate the pumping loss problem of the four-stroke gas engine have had limited success because of the limitations of the processes used. Lean burn reduces pumping loss but by relatively small amounts because of the inability to burn mixtures beyond approximately 25:1 air--fuel ratio (AFR), representing 67% additional intake-air above stoichiometry which is only 50% of total intake air at part-load where only 30% air may be required for stoichiometric combustion. This represents a pumping or throttling loss of 50% i.e. taking the intake air through a pressure drop of approximately 50% of atmospheric.
Other methods of reducing pumping loss rely on variable valve timing, as in the Miller cycle, and again these are only partially successful because they still employ a full intake and compression stroke with the accompanying mechanical frictional losses. There are also losses associated with the intake air motion in and out of the cylinder or of sequentially expanding and compressing the intake air during the valve controlled intake stoke.
General discussions on engine cycles and fuel economy are discussed in many texts, and the following are a sampling of texts which discuss these issues in some degree: "Internal Combustion Engines and Air Pollution" by E. F. Obert (Intext Educational Publishers 1973), "The Internal-Combustion Engine" by Taylor and Taylor, (International Textbook Co., 1970), and "Internal Combustion Engine Fundamentals" by John B. Heywood (McGraw-Hill Book Company, 1988).
On the other hand the present invention employs a different and shorter intake stroke, e.g. 6:1, from the expansion stroke, e.g. 12:1, to be able to, for the average driving condition, have a closer balance between the required intake air and what the piston would draw in during the intake stroke with no or limited air-throttling and with minimum mechanical friction due to the shortened intake and compression stroke. For greater air-intake either a variable intake stroke is employed providing a longer intake stroke when required, or/and an air-intake pressure boosting means is employed, e.g. a quick response compact turbocharger. The different and greater expansion stroke would assure maximum conversion of combustion heat energy to work, i.e. maximum cycle efficiency.
The present invention can be utilized with a variety of fuels including conventional petroleum-derived hydrocarbon mixture fuels, e.g., gasoline, or non-conventional petroleum and/or plant derived fuels, e.g., methanol, ethanol, natural gas, alcohol-hydrocarbon mixtures, etc. Discussion is limited to the conventional go fuels, it being understood that the points discussed herein apply to all fuels with the appropriate correction factors known to those skilled in the art.
Some terms used herein are now defined:
(1) Air-Fuel Ratio (AFR): The weight ratio of air to fuel as the vapor form equivalent of given weights of air and fuel at standard temperature and pressure (STP) in accordance with standard industry practice which takes AFR of 14.7 to one (14.7:1) as a the stoichiometric ratio for gasoline (14.7 lbs of air combusting 1 lb of gasoline).
(2) Gas-fuel ratio (GFR): It is the same as air-fuel ratio except that the component that comprises air in this case includes exhaust gas, i.e. the "gas" comprises a combination of fresh intake air and exhaust gas, where the exhaust gas may comprise "exhaust residual" remaining in the cylinder at the end of the exhaust stroke or exhaust gas recirculation (EGR) into the intake system.
(3) Lean-Burn (or Lean of Stoichiometric, or dilute charge): Operation of an engine at AFR above stoichiometric, i.e. above 15:1 AFR for gasoline engines.
(4) Stratified Charge: Generally is the purposeful formation of a non-uniform fuel-air mixture or charge in the engine cylinder prior to combustion, where a locally richer mixture is produced at the spark plug site to help ignition of an overall leaner mixture.
(5) Manifold Absolute Pressure (MAP): The absolute pressure in units of atmospheres inside the intake manifold of an IC engine beyond the throttle plate, representing the pressure of the air which is inducted into the engine cylinders. A MAP value of 1.0 represents a pressure of one atmosphere at standard temperature inside the engine intake manifold.
(6) Stroke: The displacement of the piston commencing from its one extreme position to another extreme position, which for a standard gasoline or diesel four stroke-engine comprises the sequence of equal lengths of an intake stroke, compression stroke, expansion or power stroke, and exhaust stroke.
(7) Compression Ratio (CR): The ratio of the engine cylinder displacement or volume at the beginning of the compression stroke to the displacement or volume at the end of the compression stroke. Likewise, one can define an "intake ratio" IR, and "expansion (power) ratio" EPR or PR, and an "exhaust ratio" ER.
(8) Cycle: The entire sequence of engine strokes in an IC engine which defines one complete operation of an engine cylinder, as in the four-stroke cycle, the two-stroke cycle, and the more loosely "three-stroke" cycle as defined herein to describe a way to view the current "variable cycle" engine as it is referred to.
(9) Shaft Timing: The angular position in drive shaft degrees, where one drive shaft revolution equals 360 degrees, from some reference point which herein is defined as the end of the compression stroke (also defined as top center, TC, or to remove ambiguity "shaft top center" , or "shaft TC").
(10) Stroke Timing: A specification in "stroke" degrees for a given stroke, e.g. intake, wherein the entire stroke motion is defined equal to 180 stroke degrees in a linear way, i.e. half a stroke is 90 stroke degrees independent of the actual drive shaft rotation. One drive shaft revolution of 360 degrees equals 720 stroke degrees in the preferred cam driver controlled embodiment of the invention. Top center (TC) and bottom center (BC) are defined for each stroke to correspond to the point where the piston is at the top and bottom respectively of its stroke.
(11) Ignition Timing: The degrees before top center (BTC), either in shaft or stroke degrees, where ignition commences.
(12) Valve Timing: The stroke degrees, before and after top center (BTC and ATC) where the intake valve opens and the exhaust valve closes (around the beginning of the intake stroke), the stroke degrees before bottom center (BBC) where the exhaust valve opens (before the end of the power stroke), and the stroke degrees after bottom center (ABC) where the intake valve closes (after the beginning of the intake stroke).
13) Wide Open Throttle (WOT): The operating condition of an engine in which the throttle or other means controlling air-flow into the cylinder is opened to permit essentially the maximum amount of air to enter the cylinder.
14) Throttling Loss: The engine power loss at other than WOT as a result of restricting the intake air flow causing a pressure drop across the throttle. Except where otherwise specified, the term "pumping loss" will also refer to throttling loss in the present disclosure (although it usually refers to high speed, WOT, engine air pumping loss).
Other related terms are defined below as used.